> I believe that is true but that does not explain
> why the optimum polarity setting on the receive
> end would change during a pass.
That's easy. The circularity on a pair of crossed dipoles (about all you can get on a spacecraft) May be designed for Right hand circularity when viewed from the prime direction. But by definition, that save waveform will be LHC when viewed from the opposite direction.
And since the geometry to any one observer is constantly changing by almost 180 degrees during an overhead pass, that is why it is very easy to see, complete change in circularity.
Bob, WB4APR